1. This invention is directed to a belt conveyor system, and in particular to an improved conveyor system incorporating a vacuum belt for effecting the pneumatic transfer of articles.
2. Belt conveyors for transferring articles are widely used in industry, including incorporation as integral parts of production lines, for a wide range of products. Such production lines frequently have work stations at spaced intervals, at which the conveyor is required to stop, to enable working upon the conveyed article. In such instances the precise monitoring of the displacement of the conveyor belt along its path and the lateral, horizontal positioning of the conveyed articles becomes very important. Prior systems, which monitor travel of the conveyor belt for such location purposes by encoding the revolutions of the driving motor, and which drive from an end roller, suffer from inaccuracy, due to belt slippage which generates discrepancies between rotation of the driving motor and the actual travel of the belt.
Inconsistencies in belt tension, with consequent variations in the rates of belt slippage, exacerbate this problem.
Certain types of article, for example lightweight articles having relatively large surface areas, such as plastic sheets, sheets of thin metal, cardboards, including cardboard blanks and blocks generally have smooth, low friction surfaces that make their transfer and handling most difficult. In some instances, such problems are accentuated, due to the relative fragility of the articles, or other factors such as a susceptibility to becoming marked on their surfaces, as a consequence of transfer to or passage along a conveyor, including encounter with hard stops and position sensing mechanical feelers.
The use of pneumatic transfer with conveyor systems is well known, and widely practiced, both in regard to belt conveyors and for agricultural purposes, such as the blowing of grain along pipes.
In the case of belt conveyors with pneumatic transfer many existing systems are characterized by their use of wide-area suction chambers, with associated unduly large air-mass displacement requirements, in the form of generated vacuum, or of compressed air. The response times of such systems is unduly slow, while the necessary air displacement is large, and excessive forces may be generated against system components, including the associated friction drag upon the belt, with consequent increased wear.
In other systems, the large size of certain vacuum system components necessitates unduly large belt turning radii, with correspondingly large end pulleys and related space requirements.
It should be noted that the size of a conveyor system per se, both in height and width, can bear significant economic implications, with down-sizing being most desireable. This has particular bearing on the size and location of the necessary anciliary systems associated with the conveyor.
The driving systems for conveyors usually employ a chain or other transmission acting upon the end roller of the conveyor, usually at the oncoming end. Certain disadvantages associated with these earlier arrangements include unsatisfactory frictional tractive effort between the pulley and the belt, due to the limited (180 degree or less) wrap of the belt on the pulley, and shortage of space at the conveyor end, where the motor and reduction gear are located. Also, this type of system limits and complicates the belt tensioning arrangements, as tractive transfer at the pulley is dependent upon the extent of belt wrap about the pulley, and upon belt tension.
Inadequate belt tensioning also results in excessive lost motion when the drive is reversed in order to reverse the conveyor. This exacerbates the problems encountered in achieving accurate registry of the conveyor with the associated workstations to which delivery is being made.
The handling of ferritic sheet-metal production lines has involved magnetic conveyors, which employ magnets to secure the sheet to the conveyor. There is a requirement to handle sheets of different thickness, and to permit precise manipulation of them for purposes such as the welding together of two adjoining sheets of different thickness, to form welded blanks for automotive stampings, for which operations the characteristics of magnetic attachment are not well suited.
Magnetic conveyors are also ineffective for handling aluminum or stainless steel sheet, plastic, glass, paper and cardboard, etc.
My earlier system, as disclosed in my U.S. Pat. No. 6,141,565 of Nov. 19, 2002, while overcoming many of the above-listed defects of the prior art, has been significantly improved upon, by way of the changes as set forth below.